The present application is based on Japanese Patent Application No. 2001-248919, the entire contents of which are incorporated herein by reference.
The present invention relates to a motor-operated expansion valve, and more particularly to a mechanism for avoiding welding heat applied to a valve element.
Generally, a motor-operated expansion valve consists of a main body making up a valve mechanism and a housing for hermetically sealing the valve mechanism. For example, in a three-way valve in a motor-operated expansion valve 100 shown in FIG. 13 (disclosed in Japanese Patent Publication No. JP-A-2000-310348), the opening and closing of two outflow pipes 106a and 106b are controlled by a single valve element 102 provided at a distal end of a rotor 101. Therefore, to ensure that the heat from a tungsten inert gas (TIG) welding position 104a for gastightly sealing a housing 104 and a main body 105 will not adversely affect a sliding contact surface 102a of the valve element 102, the valve element 102 is disposed in a central portion of the main body 105 which is the farthest from the welding position 104a at an outer periphery of the housing. Furthermore, to make it difficult for the welding heat from welds 105b at the outflow pipes 106a and 106b to be transmitted to the resin-made valve element 102, a thick machined part having a large thermal capacity is used for a metallic valve seat plate portion.
In addition, communicating holes 107a and 107b communicating with the two outflow pipes 106a and 106b are formed in a valve seat 105a in such a manner as to be open to a valve chamber 109, and are selectively caused to communicate with an inlet port 110 through the valve element 102 inside the valve chamber 109. As shown in FIGS. 14A to 14D, a rib 103 has a shape which surrounds a crescent recess 111, and the single valve element 102 changes over the partition of the communicating holes 107a and 107b in four modes in correspondence with the angle of rotation of the rotating shaft 101 which is displaced in response to an electrical signal sent from a stator coil 112. Namely, FIG. 14A shows a state in which the communicating hole 107a is closed and the communicating hole 107b is open; FIG. 14B shows a state in which both the communicating hole 107a and the communicating hole 107b are closed; FIG. 14C shows a state in which the communicating hole 107a is open and the communicating hole 107b is closed; and FIG. 14D shows a state in which both the communicating hole 107a and the communicating hole 107b are open.
In the mechanism shown in FIG. 13, in which the opening and closing of the two outflow pipes 106a and 106b are thus controlled by the single valve element 102, firstly, the distance between the two outflow pipes 106a and 106b is short, and the working of parts and the blazing and welding operation are difficult. Secondly, since the changeover of the four modes (open/close, close/open, open/open, and close/close) shown in FIGS. 14A through 14D is effected while the single valve element 102 is turned by one revolution, there is no leeway in the space, which makes it impossible to construct a multi-way valve of four or more ways.
Thirdly, it is impossible to independently change the flowrate control pattern of the two outflow pipes 106a and 106b, and the pattern becomes a simple one comprising only the changeover between open and close. Fourthly, since the resin-made valve element 102 is brought into pressure contact with the valve seat 105a by a spring 108, if the temperature of the metal becomes high, irregularities occur on the resin surface, and the surface roughness of the resin becomes destroyed due to heat, resulting in the occurrence of leakage in the fully closed state. Accordingly, to avoid the welding heat, it is necessary to finish TIG welding in a short time and effect rapid cooling after welding so as to minimize the effect on the resin-made valve element. For this reason, the operation requires expert skill, and uncertainty remains in the stability of quality and in reliability.
The object of the invention is to provide a valve drive device in which the above problem is overcome in a suitable manner.
To overcome the problem, there has been conceived and embodied a three-way valve 200a of a motor-operated expansion valve 200 having the construction shown in FIG. 15. Valve elements 202a and 202b are separately provided for openings 207a and 207b of outflow pipes 206a and 206b which are selectively made to communicate with an inflow pipe 210 in a valve chamber 209, and the valve elements 202a and 202b are rotated in response to inputs of electrical signals from a stator coil 212 so as to control the opening and closing of the openings 207a and 207b. 
However, since the positions of the valve elements 202a and 202b geared with and disposed radially from a pinion 203 formed integrally with a rotor 201 with respect to the two outflow pipes 206a and 206b are close to an outer peripheral portion 204a which is subject to heating by TIG welding for gastightly sealing a housing 204 and a main-body base plate 205, the resin-made valve elements 202a and 202b which are held in pressure contact with a valve seat 205a by leaf springs 208 are directly exposed to welding heat and become deteriorated or deformed, possibly resulting in faulty functioning.
In addition, consideration must also be given to the fact that the valve elements 202a and 202b are similarly affected by welding heat from welds 205b for gastightly connecting the outflow pipes 206a and 206b to the main-body base plate 205. To avoid the effect of such welding heat on the valve elements 202a and 202b, it is necessary to increase the thermal capacity by enlarging the circumference of the metallic main-body base plate 205 including the valve seat or by increasing the thickness thereof. Hence, there are problems in terms of cost and miniaturization.
In the present invention, to solve these problems, an air heat-insulation layer is formed by holding the valve element in an initial period of assembly and thereby providing a gap between the valve element and the valve seat.
In accordance with the invention, there is provided a valve drive device having a plurality of openings for communicating with an inflow pipe and an outflow pipe, said valve drive device comprising:
a valve element for opening and closing said openings;
a driving member for driving said valve element;
a rotation transmitting member for transmitting rotation from said driving member to said valve element;
a valve seat plate in which said openings are formed and on which said valve element is slid in pressure contact therewith so as to open and close said openings; and
a housing for gastightly sealing said valve seat plate and said valve element together with said driving member and said rotation transmitting member so as to form a hermetically sealed space; and
a holding device provided for tentatively retaining said valve element at a spaced-apart position spaced apart from said valve seat plate;
wherein said valve element is retained at the space-apart position when said valve seat plate and said housing are welded together.
By the above construction, an air layer extremely excelling in heat insulation is formed between the valve element and the valve seat plate, so that the valve element can be protected from welding heat, and the deformation of a sliding contact surface is prevented. Therefore, it is possible to satisfactorily maintain the sealing characteristic of the valve element.
In the invention, the holding device causes the valve element to be spaced apart from the valve seat plate in opposition to an urging device for bringing the valve element into pressure contact with the valve seat plate, the retention by the holding device is canceled after welding, and the valve element which returned to an abutment position against the valve seat plate by the urging device is spaced apart to a position in which rotating operation of the valve element for opening and closing is not interfered by the holding device. Thus, in the state in which the valve element is retained prior to effecting the starting of initial setting, the air insulating layer can be secured, and it is possible to effect the welding of the piping. In addition, the retention by the holding device is irreversible, and the valve element which has been disengaged once is disengaged completely and reliably from the holding device. The valve element upon cancellation of the retention is brought into close contact with the valve seat plate to allow the openings to sufficiently maintain gastightness, and its rotating operation for opening and closing can be effected quite freely without trouble.
Furthermore, the holding operation for retaining the valve element by the holding device is effected by the rotation of the valve element, and there is provided a restricting position for preventing the rotation at a predetermined angle of rotation. Namely, by setting the restricting position for preventing the rotation by the operation of holding the valve element by its rotation, each rotation transmitting member (gear) is retained at a position (meshing position) in which the rotation transmitting member is in a state of being interlocked with the driving member (pinion), so that the driving member (pinion) is capable of being smoothly linked with the rotation transmitting member (gear) without mutually interfering therewith. Since there is no need to adjust the angles of rotation of the gears at the time of assembly, a gear assembly jig is not required, and the assembling process can be simplified.
In addition, since the cancellation of the retention of the urging device and the valve element is effected by the operation of the valve element itself, after the valve drive device is gastightly sealed in the housing, the retention can be reliably canceled by electrical remote operation from the outside. Conversely, since the mechanical retention cannot be canceled unless the electrical operation is used, the sealing characteristic of the valve element does not deteriorate even if heat treatment is provided for the exterior fittings prior to wiring.
Furthermore, a relative angular relationship between origins of starting of the valve elements and a preventing portion provided on the rotation transmitting member for mechanically preventing the rotation at the origins of starting are uniformly defined by the restricting position. Since the proper angular position of the gear is thus ensured automatically in the assembly of parts by virtue of the restricting position, and because the number of pulses up to an electrical origin of the rotor by the pulse driving from the stator can be set in advance, the matching of origins of mechanical starting of the valve elements can be easily attained without resorting to visual observation after the valve drive device has been gastightly sealed in the housing.
Preferably, the rotation transmitting member is a gear.